In June 2015, V404 Cyg, one of black-hole binaries, underwent an outburst after 26 years of dormancy. Repetitive patterns in optical short-term variations were observed for the first time in this outburst. These patterns had been observed only in X-rays in other black-hole binaries prior to this outburst. This is an epoch-making event showing that we can see fluctuatons of radiation energy from the region close to a black hole (twinkles of a black hole) with our eye using moderate telescopes. In addition, we found the repetitive variations occured at mass accretion rate at least ten times lower than previously thought.

These figures show the twinkles of V404 Cyg. The upper figures are the actual images around V404 Cyg. The lower ones represent the light curves. The object becomes about 6 times brighter within about 1 hour.

A part of the light curves in the 2015 outburst of V404 Cyg. The vertical axis and horizontal axis represent the magnitude (brightness) and the number of days since the first day of the outburst, respectively. We can see repetitive dips with a period of about 2 hours.

click the above picture for the details

The picture is provided by Biwako Waterfall and Wetland Center.

[The current activity of V404 Cyg] fading
This object showed fading. The object got darker than at the beginning of this outburst (on Dec 23, 2015). This outburst seemed to be finished. (2016.1.7)